The present invention relates to surgical irrigation and aspiration systems for aspirating fluid from a surgical site. It more particularly relates to aspiration tubing systems used in extracapsular cataract extraction, specifically phacoemulsification. The invention further relates to phacoemulsifier aspirators models which use peristaltic pumps to achieve their aspiration function.
Intraocular surgery, and the removal of cataracts in particular, has been greatly aided by the development of surgical instruments which include cutting or fragmenting means combined with means for irrigating the intraocular surgical site and aspirating therefrom the irrigating fluid together with any tissue fragments produced by the surgical procedure. A good example of this type of system is disclosed in U.S. Pat. No. 3,589,363, to Banko et al, whose contents are hereby incorporated by reference in their entirety. Other examples of fluid control systems are disclosed in Kelman, U.S. Pat. No. 3,693,613; Weiss et al, U.S. Pat. No. 3,902,495; and Banko, U.S. Pat. No. 4,496,342; each of whose entire contents are hereby incorporated.
Basically the surgical instruments disclosed therein and particularly in the '363 Banko patent comprise a handpiece which holds an elongated ultrasonic surgical tool and contains means for exciting longitudinal ultrasonic vibrations in the tool. The vibrating tool when applied to tissue, such as a crystalline lens of the eye which has developed a cataract, is capable of breaking the tissue into small pieces. The tool is provided with a means for supplying an irrigation fluid to the surgical site and an aspiration means for removing the irrigation fluid and fragmented tissue from the surgical site. The aspiration means includes an axial bore through the ultrasonic tool which is connected to a source of suction whereby the tissue fragments are aspirated from the surgical site, together with the irrigation fluid. Because the ultrasonic surgical tool fragments the excised tissue into very small particles, which are removed with the spent irrigation fluid, the incision of the eyeball need be only large enough to insert the tool therein and is substantially smaller than the incision required for removing the lens in one piece. However, since the surgical wound in the eyeball is only large enough to insert the ultrasonic surgical tool and irrigation means, the surgical field is practically entirely enclosed, and controlling the flow therethrough of irrigation fluid and aspiration fluid is very important. In particular, the suction applied to the aspiration means must be limited to a safe value, to avoid the danger of collapsing the eyeball. A blockage or occlusion may occur, for example, when a piece of fragmented tissue which is larger than the axial bore of the surgical tool is drawn against the entrance to that axial bore. When such a blockage occurs in the aspiration line, the negative pressure or suction in the aspiration conduit between the surgical site and the vacuum pump increases. If the blockage is then suddenly released either by the mechanical action of the ultrasonic tool or by the increased value of the suction force, there is a tendency for the fluid within the surgical site to rush suddenly into the aspiration conduit with perhaps disastrous consequences. This is an especially important problem in ocular surgery because the total volume of the fluid in the surgical site is smaller than the volume of fluid in the irrigation and aspiration lines.
Generally, the systems of the above-mentioned patents which utilize vacuum control systems consisting of on/off solenoid valves and relief valves were not capable of sensing a blockage in the aspiration conduit and then rapidly and positively, under the control of the surgeon, equalizing the pressure in the irrigation and aspiration lines for rapid clearing of a blockage. Accordingly, a new fluid control system was developed and it is set forth in application Ser. No. 865,360, which is now abandoned and was replaced by U.S. application Ser. No. 105,978 that issued as U.S. Pat. No. 4,832,685 on May 23, 1989, of S. W. Haines, whose contents are hereby incorporated by reference in their entirety. The fluid control system defined therein for a surgical irrigation/aspirator allows the excess vacuum in the aspiration tubing after a blockage to be controllably and rapidly released by venting to the irrigation line and not to air. This liquid venting or pressure equalization system provides a faster rise time, reduces the chance for mini collapses of the enclosed surgical site (eye) to occur, and further requires only one irrigation bottle and the use of a check valve to prevent reversed irrigation flow towards that bottle when venting.
In the past it has been known to use a vacuum pump to create a vacuum and thereby achieve aspiration, as is disclosed for example in the Storz Microvit Vitrectomy System. Vacuum pumps though are susceptible to fluid contamination and, as such, precautions must be made to minimize contact of the aspirant with the pump such as by the use of hydropholic filters on the pump input (the vacuum side thereof) and/or electronic devices which sense and warn of excessive fluid levels. Accordingly, peristaltic pumps are now preferred because of their lack of contamination, their good controllability, their relatively high suction capability and the ease with which the pump can be stopped without special provision for avoiding back flow. Such peristaltic pump systems are disclosed in the above-mentioned U.S. patent and also in U.S. Pat. No. 4,713,051 issued Dec. 15, 1987 to D. L. Steppe et al., whose contents are hereby incorporated by reference in their entirety. In the last-mentioned system a surgical cassette is disclosed which achieves aspiration by means of cooperating with a rotary peristaltic pump mounted on a cassette mechanism integral to the control unit.
Peristaltic pumps function by sequentially compressing a segment of tubing between a fixed plate and moving plate (linear) or rollers (rotary), and this motion moves a bulbous of fluid or tissue from the operative site. The plates or rollers are so arranged so that at any time at least one is occluding the tubing against the fixed plate. As the moving plate or roller engages the tubing, a transient pressure increase (TPI) is experienced in the tubing which peaks when the moving plate or roller is fully engaged against the tubing and fixed plate. This TPI decreases to the steady state level until the engagement of the next moving roller or plate against the tubing. The frequency of these TPI's is dependent on the speed of the peristaltic pump, and the amplitude and the capacitance of the system.
By replacing the column of air that was between the pump and the eye with liquid venting to make the system more responsive the air column which acted as a shock absorber for the pump was thereby removed. As mentioned above peristaltic pumps by their operation cause a roller to come in contact with tubing which displaces the fluid at both ends of the tubing by compressing the tubing. Since the above-mentioned fluid venting system has no air in the tubing and due to the fact that the liquid will not compress or expand, turbulence in the eye results. In other words, oscillating turbulence in the eye from the pump will be seen when there is no occlusion in the aspiration line since there is nothing restricting the large variance of flow that is transmitted to the eye. (If there is an occlusion in the aspiration line the oscillation will not be seen because there is high resistance in the line or no flow at all in the eye.) This oscillating turbulence in the eye, due to the changing pressure in the eye, causes the iris to flap around (so called "iris flutter") and the posterior capsule to bounce up and down, both of which movements are undesirable. It is therefore an object of this invention to increase the capacitance of the system while retaining the increased fluidic response gained by the new technologies employed in the vacuum control system.
Thus, a need has arisen for an improved irrigation and aspiration system which remedies these problems of prior systems.